2
Herpetozoa 38: 137-153 (2025)
O G = H e i peto ZO a DOI 10.3897/herpetozoa.38.e143411
Austrian Herpetological Society
Expanding habitat suitability under changing climate
and land use may drive rapid expansion of Russell's viper
(Daboia russelii) in Bangladesh
Najmul Hasan", Joya Dutta'?, Mohammed Noman??*, Md. Mizanur Rahman"**, Sajib Rudra**,
Abdul Auawal?*, Md. Rafiqul Islam??*, Md. Asir Uddin?**, Harij Uddin'*?, Md. Towfiq Hasan",
Md. Farid Ahsan'**, Ulrich Kuch?”?, Aniruddha Ghose**®, Ibrahim Khalil Al Haidar’,
Mohammad Abdul Wahed Chowdhury'*:3*
Department of Zoology, University of Chittagong, Chattogram 4331, Bangladesh
Venom Research Centre, Chittagong Medical College, Chattogram 4203, Bangladesh
Eco-climate Lab, Department of Zoology, University of Chittagong, Chattogram 4331, Bangladesh
Animal Immunization Lab, University of Chittagong, Chattogram 4331, Bangladesh
Institute of Occupational, Social and Environmental Medicine, Goethe University Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt am Main,
an FF WN
Germany
6 Department of Medicine, Chittagong Medical College, Chattogram 4203, Bangladesh
https://zoobank. org/C6E28572-2060-4164-BE00-7EB3CF58FCE4
Corresponding authors: Ibrahim Khalil Al Haidar (ibrahimalhaidar88@gmail.com); Mohammad Abdul Wahed Chowdhury (piloctg@yahoo.com)
Academic editor: Philipp Wagner @ Received 4 December 2024 @ Accepted 22 May 2025 ¢ Published 17 June 2025
Abstract
Eco-climatic and other environmental gradients significantly influence the geographic distribution of reptiles. In Bangladesh, the
known range of Russell’s viper (Daboia russelii) has expanded extensively in recent decades. Using species distribution model-
ling, we analysed habitat suitability, dispersal pathways, interspecific competition, and population dynamics to explore the drivers
behind this phenomenon. Our findings indicate a five-fold increase in climatically suitable area (76,716 km?) since 2015, attributed
to higher cold-season temperatures and increased dry-season precipitation, facilitating the viper’s spread into previously unoc-
cupied regions. The rapid dispersal of these snakes may have benefited from the strong currents of rivers, channels and seasonal
waterways, and flat floodplain terrain. Additionally, the extension of agricultural and grassy habitats in new regions has provided
abundant rodent prey and minimal predator or competitor pressures, creating ideal conditions for population growth. We also ob-
served a female-biased population structure and large clutch sizes which may have further accelerated reproduction, contributed to
rapid population expansion. In rural Bangladesh, where clinicians face multiple problems with the management of Russell’s viper
envenoming, increasingly frequent human encounters with this highly dangerous snake have caused great public concern. Despite
the observed range expansion, the species also faces challenges such as unsuitable temperature fluctuations, reduced precipitation
in some regions, and anthropogenic threats, including anti-snake attitudes and killings. Given the increasing risk of human-snake
conflicts, implementing effective snakebite management plans and conservation strategies is crucial to safeguard public health while
ensuring the survival of this ecologically and economically important predator of rodents.
Key Words
Eco-climatic parameters, female-dominant population, geospatial parameters, land use, range expansion, rice cultivation, river
networks, snake, species distribution model, Viperidae
Copyright Najmul Hasan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License } PENSUFT.
(CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source
are credited.
138 Najmul Hasan et al.: Expanding habitat suitability of Russell's viper in Bangladesh
Introduction
Russell’s viper, Daboia russelii (Shaw & Nodder, 1797),
is a medically important venomous snake species with a
very wide geographic distribution in South Asia (Warrell
and Williams 2023). This species belongs to the medically
most significant snakes worldwide due to its common oc-
currence in agricultural lands, prompting frequent human
encounters and snakebites, highly toxic and geographical-
ly variable venom, and complex syndrome of envenom-
ing which is difficult to treat and results in severe mor-
bidity with high rates of mortality and disability (Warrell
1989; Alirol et al. 2010; Pla et al. 2019; Senji Laxme et
al. 2021). Daboia russelii has usually been reported as be-
ing wide-ranging across Pakistan, India, Sri Lanka, Ban-
gladesh, Nepal, and Bhutan (e.g., Suraj et al. 2021), but
the distributions of D. russelii and its Southeast and East
Asian sister species Daboia siamensis (Smith, 1917) are
actually patchy and discontinuous, suggesting important
climatic and other environmental effects on the occurrence
of these large vipers (Wuster 1998 , Warrell and Williams
2023). While a series of short snakebite case reports at-
tributable to this species pointed to its presence in western
and northern Bangladesh in the 1920s, no specimens or
suspected or proven bites by D. russelii had been estab-
lished to have occurred in this country until 2013 despite
extensive efforts to find them (Banerji 1929; Kuch 2007;
Amin et al. 2024a, b), suggesting that its populations in
Bangladesh might have experienced declines in the late
20" century. As a result, D. russelii was assessed as Criti-
cally Endangered (CR) in 2000 (IUCN Bangladesh 2000).
However, following its rediscovery in 2013 and 2014, a
subsequent reassessment shifted the status of D. russelii
to Near Threatened (NT) (Rahman 2015). In the follow-
ing years, these vipers have been recorded from multiple
additional localities and regions of Bangladesh, often in
connection with claims by local peoples that such snakes
had not been seen before in their areas, which suggests an
ongoing range expansion (Ahsan and Saeed 2018; Haidar
et al. 2023; Amin et al. 2024a, b). Initially documented in
six administrative districts until 2015 (Rahman 2015), D.
russelii has since been recorded in 27 out of 64 districts in
Bangladesh (Amin et al. 2024 a, b). Over the same period,
the number of snakebite incidents and deaths caused by
this species has surged in Bangladesh (Haidar et al. 2023;
Amin et al. 2024a, b), emphasising the need for addition-
al research to investigate the dimensions and background
of this public health emergency. Although several stud-
ies focusing on the biomedical aspects of D. russelii in
Bangladesh have since been initiated, the ecological ram-
ifications of its apparent expansion in this country have
remained relatively unexplored.
Species distribution and range dynamics are heavily
influenced by a species’ acclimatisation potentiality, eco-
logical preference, and environmental gradient (Wiles
et al. 2003). In addition, range expansions may disrupt
ecological equilibrium by increasing competition for
ecosystem resources. Thus, understanding the ecological
herpetozoa.pensoft.net
factors driving range expansion and population surges is
essential for devising effective conservation and man-
agement strategies (Villero et al. 2017; Chowdhury et al.
2021). As a venomous snake species, D. russelii presents
a dual challenge: Its range expansion not only raises pub-
lic health concerns due to frequently severe and fatal en-
venoming (Senji Laxme et al. 2021) but also necessitates
better knowledge of its ecological requirements and dis-
tribution to inform snakebite management policies.
Habitat suitability, determined by vegetation types
(Rondinini et al. 2011), resource availability (Tschumi
et al. 2020), and ecological services (LOpez-Lopez et
al. 2007), plays a pivotal role in shaping species distri-
bution (Muthoni et al. 2010). Anthropogenic activities,
such as agricultural land use (Reverter et al. 2021), can
profoundly alter these habitat characteristics (Bodo et al.
2021), impacting species presence (Pomara et al. 2014).
Climate change further intensifies these pressures by
altering habitat suitability (Archis et al. 2018; Zacarias
and Loyola 2019), and associated ecological dynamics
(Bastille-Rousseau et al. 2018), affecting species be-
haviour (Du et al. 2023), reproduction (Both and Viss-
er 2001), and population trends (Pomara et al. 2014). In
climate-vulnerable countries like Bangladesh (Harmeling
2008), these changes hold particular relevance for poiki-
lothermic species like snakes (Chowdhury et al. 2022).
Species distribution modelling has emerged as a powerful
tool for investigating suitable niches (Hirzel et al. 2002;
Mizsei et al. 2016, 2021) by considering various climate
and geo-spatial variables. These statistically robust mod-
els allow us to predict the suitable habitat of a species
for present, past, and future global scenarios (Jarvie and
Svenning 2018; Park et al. 2022). Understanding the in-
tricate relationships between snakes and eco-climatic and
spatial factors is crucial for predicting species responses
to environmental changes and their potential distribution.
Additionally, predator-prey relationships and interspecif-
ic competition are critical for regulating population dynam-
ics and shaping community structures (Terborgh and Estes
2013; Mukherjee 2020). Predators act as population regula-
tors, while competition influences species coexistence and
resource partitioning (Pontarp and Petchey 2018; Radovics
et al. 2023). Investigating the roles of predators and com-
petitors in the habitats of D. russelii may provide insights
into its apparent rapid range expansion in Bangladesh.
The country’s subtropical environment, character-
ised by extensive floodplains and diverse habitats, sup-
ports rich biodiversity but also poses unique challenges.
Frequent flooding (Kabir and Hossen 2019), facilitated
by its low-lying topography and dense river networks
(Khalid 2010), creates temporary aquatic corridors that
enable the dispersal of species like D. russelii (Lesack
and Marsh 2010). Snakes are known to disperse actively
during flood events by leveraging their swimming abili-
ties to move across flooded areas and explore and colo-
nize new lentic habitats (Poiani 2006; Chowdhury et al.
2022). Moreover, agricultural fields provide ample prey,
such as small mammals, and concealment in undergrowth
Herpetozoa 38: 137-153 (2025)
(Halstead et al. 2019), thus serving as prime habitats for
many terrestrial venomous snakes including this viper
(Warrell 1989; Glaudas 2021). Villagers are often en-
countering D. russelii while working in their agricultural
fields, exacerbating human-snake conflict (Haidar et al.
2023; Amin et al. 2024a, b).
In this study, we employed species distribution mod-
elling to evaluate the apparent rapid range expansion
of D. russelii in Bangladesh. By predicting current and
future climate suitability and analysing factors such
as land use changes, predator-prey dynamics, and dis-
persal pathways, we aim to provide a comprehensive
understanding of its ecological requirements. Our find-
ings will support the development of effective conser-
vation strategies and snakebite management plans, ad-
dressing both species preservation and public health
concerns in Bangladesh and beyond.
Materials and methods
Study area
This study was conducted across the entire mainland
of Bangladesh (Fig. 1B), situated between 23°41'N
and 90°20'E, with a total land area of approximately
147,570 km? (Rashid 2019). Positioned at the confluence of
the Indo-Himalayan and Indo-Chinese sub-regions within
the Oriental biogeographic realm, Bangladesh serves as a
critical corridor for species migration between the Indian
subcontinent and Southeast Asia (Khan 2018). Its inclu-
sion in the Indo-Burma biodiversity hotspot underscores
its global ecological significance (Myers et al. 2000).
Bangladesh experiences a subtropical monsoon cli-
mate, marked by three distinct seasons: pre-monsoon
(March-May), monsoon (June to October), and winter
(November to February), with heavy rainfall dominating
the monsoon period (Rashid 2019). Its landscape is pre-
dominantly shaped by the dynamic river systems of the
Brahmaputra, Ganges (Padma), and Meghna, forming an
extensive riverine and deltaic terrain (Sarker et al. 2016).
The ecological diversity of Bangladesh is reflected in
its 12 bio-ecological zones (Nishat et al. 2002), seven cli-
matic sub-regions (Rashid 2019; Chowdhury et al. 2022),
and five distinct forest types, encompassing tropical and
subtropical ecosystems (Henry et al. 2021). This combi-
nation of climatic variability and topographic complexity
makes Bangladesh an ideal region for studying ecological
processes and species distribution patterns.
Species occurrence data
A trained snake rescuer team has been actively rescuing
D. russelii from the western regions of the country from
2019 to 2023 through a continuous field survey and re-
sponding to the rescue call. The specimens of D. russelii
were collected randomly from various locations along
Ie
with their habitat notes, highlighting its occurrence in
previously unreported areas. We compiled a total of 231
occurrence points of D. russe/ii from three sources: field
collections, research-grade database, and reliable print
or electronic media (Fig. 1B). Between 2019 and 2022,
69 specimens were collected through active field work
across various localities in Bangladesh under a permit
from the Bangladesh Forest Department (permission let-
ter no: 22.01.0000.101.23.2019.3173). These specimens
are currently housed at the Venom Research Centre, Ban-
gladesh, and were documented with detailed informa-
tion, including collection date, geographical coordinates,
sex, and morphological characteristics. To supplement
this dataset, area of occupancy (AOO) polygons were
obtained from the IUCN Red List assessment (Rahman
2015), and 100 random occurrence points were collect-
ed from these polygons. Additional verifiable data were
obtained from global biodiversity repositories such as
GBIF (GBIF Secretariat 2023) and iNaturalist (iNatural-
ist 2024). After rigorous validation and cross-referencing,
we incorporated 62 occurrence points derived from liter-
ature, preserved specimens, and authenticated sources in
print, electronic, and social media.
Variables for suitable niche analysis
We obtained 19 bioclimatic variables from WorldClim
2.0 at a spatial resolution of 30 arc-seconds (approx-
imately 1 km? grid cells) for both current (1970-2000)
and future (2061—2080) climate scenarios (Hijmans et al.
2005). To ensure consistency and minimise biases due
to varying measurement scales, all variables were stan-
dardised using z-score transformation. Highly correlated
variables (correlation coefficient, r > 0.9) were exclud-
ed to address multicollinearity concerns (De Marco and
Nobrega 2018), resulting in a final selection of 12 biocli-
matic variables (Table 1). Future climate suitability for
D. russelii was modelled using 23 climate projections
for 2080 based on the shared socioeconomic pathway
370 (ssp370) scenario (Masson-Delmotte et al. 2021).
All vector and raster datasets were prepared within the
WGS§84 coordinate system and clipped to match Bangla-
desh’s geographical boundaries.
In addition, seven spatial variables (e.g., bio-ecolog-
ical zones, climatic sub-regions, elevation, flood plains,
forest types, land use, and river zones) were included in
the analysis (Table 1). These datasets were converted into
raster format following the methodologies by Chowd-
hury et al. (2022) and Dutta et al. (2024). Autocorrelation
tests confirmed that the spatial variables were indepen-
dent. The 12 bio-ecological sub-zones and seven climat-
ic sub-regions were digitised from published literature
(Nishat et al. 2002; Rashid 2019). Floodplain and river
zone data were sourced from the Bangladesh Agricultur-
al Research Council (Bangladesh Agricultural Research
Council 2019) and the Water Development Board, as
cited by Sarker et al. (2016).
herpetozoa.pensoft.net
140 Najmul Hasan et al.: Expanding habitat suitability of Russell's viper in Bangladesh
Table 1. Twelve bioclimatic and seven spatial variables used
in this study.
No. Variable Description Category
Name
1 ~~ Bioclim 1 Annual mean temperature (°C) Temperature
2 Bioclim2 Mean diurnal range (mean of monthly
(max temp.-min temp. ))
3. ~—- Bioclim 3 Isothermality (Bio02/Bi007) x 100
4 Bioclim 4 Temperature seasonality (standard
deviation x 100)
5 Bioclim 5 Max. temperature of
warmest month (°C)
6 Bioclim6 Min. temperature of coldest month (°C)
7 Bioclim 7 Temperature annual range (Bio05-
Bio06) (°C)
Annual precipitation (mm)
Precipitation of driest month (mm)
Precipitation seasonality
(coefficient of variation)
Precipitation of driest quarter (mm)
Precipitation of warmest quarter (mm)
8 Bioclim 12
9 Bioclim 14
10 Bioclim 15
Precipitation
11. ~=Bioclim 17
12 Bioclim 18
13. Spatial 1 Elevation Topography
14. Spatial 2 Bio-ecological zones Ecological
15 Spatial 3 Climatic sub-regions Climate
16 Spatial 4 Flood plain Hydrological
17. Spatial 5 Forest types Ecological
18 Spatial 6 Land use Land use
19 Spatial 7 River zones Hydrological
Elevation data were collected from the Earth Resources
Observation and Science Centre using SRTM 3 arc-second
(90 x 90 m? ) datasets (United States Geological Survey
2019). Land use and land cover data, with a spatial resolu-
tion of 100 x 100 m2, were obtained from the Copernicus
Global Land Service (Buchhorn et al. 2019). Forest cover
data, at a resolution of 30 <x 30 m’, were acquired from
the Bangladesh Forest Department repository (Henry et
al. 2021). All raster datasets were resampled to a standard
resolution of 1 km? using the nearest neighbour resampling
technique in the ArcGIS environment. These datasets fea-
tured categorical pixel values to represent distinct environ-
mental attributes. For example, the flood raster categorised
pixels as either outside the flood zone (value = 1) or within
it (value = 2). Similarly, five other variables—bio-ecolog-
ical zones, climatic sub-regions, forest zones, land use,
and river zones—had complex categorical structures, with
varying numbers of categories per raster file. This cate-
gorisation provided a detailed representation of the envi-
ronmental characteristics across the study area, supporting
comprehensive ecological analyses.
The spatial and temporal dispersion patterns of D. rus-
selii were analysed using 69 field-collected occurrence re-
cords. To evaluate yearly range expansion, the occurrence
data were organised chronologically and visualised using
ArcGIS. Each record was sorted by year and mapped at
the district level, with newly recorded districts added incre-
mentally for each subsequent year. This stepwise approach
enabled a progressive mapping of the viper’s distribution
across Bangladesh over time. By examining the assumed
yearwise distributional changes, potential routes of dis-
persion were inferred. This provided insights into possible
herpetozoa.pensoft.net
geographic pathways and expansion trends of D. russelii,
highlighting areas of recent colonisation and facilitating the
identification of ecological factors driving this expansion.
Species distribution model
To predict the suitable climatic niches of D. russelii in
Bangladesh, we utilised Species Distribution Modelling
(SDM) following the methodology described by Ran-
gel and Loyola (2012). Initially, the six distinct spatial
variables with categorical values—bio-ecological zones,
climatic sub-regions, flood plain, forest types, land use,
and river zones—were converted to raster with continu-
ous values. This was done by calculating the proportion
of the area of each category under the species’ Area of
Occupancy (AOO). First, each categorical raster was
masked using the AOO of this viper, retaining the num-
ber of categorical cells within the species’ AOO. The pro-
portion of the AOO area within each category was then
calculated to produce a category-specific percent occu-
pancy. The percent occupancy values were then used to
reclassify the categories by replacing each category value
with the corresponding percent occupancy. For example,
if the AOO of this viper species distributed 40% over the
cells of category A and 60% over the cells of category
B of a spatial raster, we assigned 0.4 to all cells of cat-
egory A and 0.6 to all cells of category B. The rest of
the cell of that raster was assigned as 0. Finally, raster
stack of 19 variables (Table 1) were used to perform the
species distribution model.
We employed the Bioclim() and the Maximum Entro-
py Maxent() algorithms to determine the suitable climate
space for D. russelii in Bangladesh. The Bioclim() is a
simple and non-parametric approach suitable for pre-
dicting climate-driven niches (Beaumont et al. 2005;
Hallgren et al. 2019), while the Maxent() model is a ma-
chine-learning algorithm to determine the suitable cli-
mate space for D. russe/ii in Bangladesh (Phillips 2021).
We used the “‘DISMO’ (Hijmans et al. 2017) and ‘RJAVA’
(Urbanek 2024), “MAXNET?’ (Phillips 2021) packages on
R platform (version 4.4.1) with the integration of several
supporting packages, including “RASTER’ (Hijmans and
Van Etten 2019), ‘MAPTOOL (Bivand et al. 2016), “‘RG-
DAL’ (Bivand et al. 2019), ‘SP’ (Pebesma and Bivand
2019) and ‘SF’ (Pebesma 2018). This approach provided
a robust framework for identifying potential climate-driv-
en habitats of D. russelii, facilitating further analysis of
its distribution dynamics across Bangladesh. To ensure
transparency, reproducibility, and comprehensive docu-
mentation of the species distribution modelling process,
we followed the ODMAP (Overview, Data, Model, As-
sessment, and Prediction) protocol (Zurell et al. 2020).
ODMAP provides a standardised framework for doc-
umenting each step of the modelling workflow, from
data collection and pre-processing to model develop-
ment, evaluation, and prediction. By adopting this struc-
tured approach, we aimed to enhance the clarity of our
methodological decisions and facilitate future replication
Herpetozoa 38: 137-153 (2025)
or extension of our study (Suppl. material 2). The models
were evaluated using the area under curve (AUC), thresh-
old-dependent sensitivity, specificity, and Cohen’s Kappa.
Suitable and unsuitable area analysis
For this analysis, we first reclassified the predicted raster
outputs from both the Bioclim and Maxent models using
Ensembled .,.,envfuture)
The resulting ensembled raster was then reclassified
into three distinct categories to indicate climatic suitabil-
ity. To determine the threshold, we multiplied the thresh-
old values from each model by their respective weights.
For example, the threshold probability for the Bioclim
prediction in the current climate is 0.0022, and for Max-
ent, it is 0.1356. Thus, the weighted threshold for the cur-
rent climate is: (0.3 x 0.0022) + (0.7 x 0.1356) =0.09558.
This weighted threshold was used to reclassify the en-
sembled predictions into three categories:
¢ Cells with no occurrence probability were assigned
a value of 0.
¢ Cells with probability values from —oo to 0.09558
were classified as 1 (unsuitable areas).
¢ Cells with probability values greater than 0.09558
were classified as 2 (suitable areas).
A similar process was applied to future climate model
predictions, where the following categories were used:
¢ Cells with no occurrence probability were assigned
a value of 0.
¢ Cells with probability values from —oo to 0.03984
were classified as 3 (unsuitable areas).
¢ Cells with probability values greater than 0.03984
were classified as 6 (suitable areas).
This reclassification enabled a clear categorization of
each cell within the raster for both the current and future
climate conditions. To facilitate direct comparison between
current and future suitability, we then overlapped the raster
files from both time periods and summed the corresponding
cell values to generate distinct integer values, as follows:
Future unsuitable (3) Future suitable (6)
Currently 1+3 =4 (Common 1+6 = 7 (Currently
unsuitable (1) unsuitable) unsuitable, future suitable)
Currently 2+3 = 5 (Currently 2+6 = 8 (Common suitable)
suitable (2) suitable, future unsuitable)
Principal component analysis for
identifying influential climatic factors
To identify the key factors influencing the distribution
of D. russelii in Bangladesh, we performed a Principal
Component Analysis (PCA) using SPSS, following the
= (0.3 x reclassified Bioclim
(current/future)
141
their respective threshold values. Cells with values above
the threshold were assigned a value of 1 (indicating suit-
able areas), while cells with values below the threshold
were assigned 0 (indicating unsuitable areas). These re-
classified raster files were then ensembled. Since Maxent
provided more realistic predictions with higher and more
consistent AUCs for both current and future climate sce-
narios, it was assigned a higher weight in the ensemble
operation. The ensemble formula was as follows:
) + (0.7 x reclassified Maxent meta)
methodology described by McGarigal et al. (2000). PCA
is a robust statistical tool that reduces dimensionality by
identifying the most important variables that account for
the maximum variance in a dataset. This allows us to
isolate the climatic factors that most significantly drive
the species’ distribution (Bueno de Mesquita et al. 2021;
Joswig et al. 2022). Data were collected for 13 predictor
variables, including 12 bioclimatic variables and eleva-
tion, at the occurrence points of D. russelii. Addition-
ally, six spatial variables were converted from categor-
ical to continuous format by calculating the percentage
occupancy of each category within the species’ known
range in Bangladesh. This transformation ensured con-
sistency across variables, enabling a more accurate PCA.
The results of the PCA highlighted the relative impor-
tance of climatic and environmental variables, providing
valuable insights into the ecological drivers of the dis-
tribution of D. russelii and guiding subsequent habitat
modelling efforts.
Sex ratio analysis
From 2019 to 2022, 61 vipers were collected during field-
work and through rescue operations. Their sexes were de-
termined using sex determination probes following estab-
lished methodologies (Marais 1984; Mader 2006). This
analysis aimed to evaluate the population’s sex ratio and
its demographic structure over multiple years. However,
data from 2022 and 2023 were excluded from the anal-
ysis due to incomplete records. By determining the sex
ratio, we gained insights into the population dynamics
of D. russelii, which could have implications for under-
standing its reproductive ecology.
Analysis of predators, competitors,
habitat, and annual floods
Animals known to prey on snakes were identified as poten-
tial predators of D. russelii. Information on the conservation
status and population trends of these predators (Suppl. ma-
terial 3) was sourced from published literature, including the
Red List of Bangladesh Volumes 2, 3, and 4 (IUCN Bangla-
desh 2015 a, b, c). Similarly, potential competitor species
were identified based on their dietary overlap and shared
habitat preferences with D. russelii (Suppl. material 4).
herpetozoa.pensoft.net
142 Najmul Hasan et al.: Expanding habitat suitability of Russell's viper in Bangladesh
Data on these possible competitors were gathered by ana-
lysing their feeding habits, behaviours, and geographic dis-
tributions as described in the same literature sources.
To assess habitat conditions, data on rice production and
paddy fields, which serve as primary habitats for D. russelii,
were collected from the Yearbook of Agricultural Statistics
(Bangladesh Bureau of Statistics 2023) spanning the years
2012 to 2022. Additionally, information on annual floods,
a key factor influencing snake dispersal and habitat dy-
namics, was extracted from the Annual Flood Report 2021
published by the Bangladesh Water Development Board
(Barua et al. 2021). This multi-faceted approach enabled
a comprehensive understanding of the ecological factors
influencing the expansion and population trends of D. rus-
selii, providing insights into its interactions with predators,
competitors, and its flood-prone habitat.
Data resources
The data underpinning the analysis reported in this paper
are deposited at GBIF, the Global Biodiversity Informa-
tion Facility, and are available at https://ipt.pensoft.net/
resource?r=russells_viper_bangladesh.
Results
Pattern of dispersion
Our field observation found that D. russelii might be dis-
persed through two possible ways—one exploiting aquat-
ic channels and the other relying on terrestrial plains—
enabling the species to expand its range across previously
unoccupied habitats. As of 2019, the species’ distribution
was primarily concentrated in the north-western regions
of Bangladesh along the Padma and upper Meghna Rivers
(Fig. 2A). From 2019 to 2021, dispersion was observed
through riverine channels, where individuals moved from
the upper to the lower Meghna River (Fig. 2B, C). This
pathway might enable the viper to colonise new river-
side localities, including tidal floodplains and coastal
islands within the Bay of Bengal. On the other hand,
sightings recorded in previously unoccupied localities
such as Meherpur, Jhenaidah, and Chuadanga by 2022
can be deduced as terrestrial dispersion (Fig. 2D). By
2023, D. russelii had reached Satkhira, a coastal district
in southwestern Bangladesh, through terrestrial corridors
that included crossings via Jashore district (Fig. 2E).
Current and future suitable climate
spaces
Climate model analysis revealed that D. russelii cur-
rently has a broad suitable climatic area of approxi-
mately 76,716 km? in western Bangladesh (Fig. 3A, B).
herpetozoa.pensoft.net
However, projections for 2080 indicate a slight reduction
in this suitable space for this viper. Across both present
and future scenarios, approximately 75% of the study
area remains unsuitable for D. russelii (Fig. 4).
Currently, the estimated suitable climate space
(Fig. 3A, B) is nearly five times larger than the species’
observed area of occurrence (AOO: 14,344 km/7). These
areas are predominantly located along major river sys-
tems, including the Padma, Meghna, and Jamuna, and en-
compass regular floodplains, low tidal plains, and diverse
forest types such as tropical deciduous, mangrove, and
village forests.
The current suitable climate space of D. russelii in
Bangladesh is confined to the western half of the country.
According to the weighted ensemble of predicted models
(Maxent and Bioclim), the major portion of the suitable
Space 1s situated at the banks and char lands of the Padma,
Meghna, and the Jamuna River. Most of these areas are
riverbanks, and lower flat plains, and cover the major por-
tion of the village forest of the southern, central, north-
west and northern part of the country.
The river bank area of the north-west and central parts
is the most suitable place for this viper (p > 0.6) under the
current climate scenario (Fig. 3A), but its suitability is
slightly reduced in 2080 (p < 0.4) (Fig. 3B). The southern
coastal area and the mangrove forest also provide current
suitable space (0.4 > p < 0.6), but reduced in the future
(p < 0.2) (Fig. 3A, B).
Both Bioclim and Maxent models strongly support
that the riverbank, char lands, and lower floodplains of
Padma, Meghna and Jamuna rivers of the country pro-
vide the current suitable climatic condition for D. russelii
in Bangladesh (p > 0.8 for Maxent, 0.5 for Bioclim). In
the future (2080), this suitable climate situation slightly
decreases (p < 0.005 for Bioclim and p < 0.5 for Maxent)
(see details in Suppl. material 5).
Model evaluation
The Bioclim model proved to be highly effective in the
current climatic condition, with high discriminatory
power (AUC = 0.9851), in addition to high sensitivi-
ty (0.9821) and specificity (0.9739), thus indicating its
ability to correctly differentiate between suitable and un-
suitable climate space. However, its performance signifi-
cantly declined when tested against future climate scenar-
ios (AUC = 0.6512), as indicated by the low specificity
(0.3087) and low Kappa value (0.3054) (Table 2).
In contrast, the Maxent model showed consistently
strong performance in both the current and future con-
texts, as evidenced by consistent AUC values (0.9730 for
the present context and 0.9718 for the future context),
maximum sensitivity (1.0), and high specificity (0.9522)
in both cases. This highlights the ability of Maxent to clar-
ify complex environmental interactions and its resilience
to changing climatic conditions, thus making it a more
Herpetozoa 38: 137-153 (2025) 143
A B
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\ Afghanistan _ Z
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As LL So IE eee er a,
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ey Zz
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a
g
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S | __ Distribution of Daboia russelii in Asia pS
= }
Maldives
60°0'0"E 70°0'0"E 80°0'0"E 90°0'0"E 89°0'0"E 91°0'0"E 93°0'0"E
E H I
C D
Figure 1. A. Distribution of Daboia russelii in Asia (Suraj et al. 2021); B. Occurrence points of D. russelii used for species dis-
tribution modelling; C. 12 bio-ecological zones (Nishat et al. 2002); D. Seven climatic sub-regions (Rashid 2019); E. Elevation
(United States Geological Survey 2019); F. Flood plain (Bangladesh Agricultural Research Council 2019); G. Forest zones (Henry
et al. 2021); H. Land use types (Buchhorn et al. 2019); I. River zones (Sarker et al. 2016). The details of the seven spatial variables
are provided as Supplementary material 1.
Table 2. Comparative performance evaluation of Bioclim and Maxent models in predicting the potential distribution of Daboia
russelii under current and future (2080) scenarios in Bangladesh.
Model AUC Threshold
Bioclim (Current) 0.9851 0.0022
Bioclim (Future) 0.6512 0.0005
Maxent (Current) 0.9730 0.1356
Maxent (Future) 0.9718 0.0567
reliable tool for predicting the distribution of D. russelii
in future contexts (Table 2).
The SDM analysis for D. russelii in Bangladesh shows
that 23% of the country’s land is climatically suitable,
while 77% is unsuitable. Future projections reveal that
21% of the land will be suitable, compared to 79% that
will remain unsuitable. The areas found to be suitable in
the current and future evaluations include 19%, while
76% of the country is unsuitable in both temporal anal-
yses. Additionally, about 4% of the currently suitable ar-
eas are expected to shift to an unsuitable category, while
about 1% of the areas found to be unsuitable will be suit-
able in the future (Fig. 4).
Despite these changes, the regular floodplain remains
a consistent feature within both present and future suit-
able climatic spaces, underscoring its importance as a
stable habitat component for D. russe/ii in Bangladesh.
Sensitivity Specificity Kappa
0.9821 0.9739 0.9558
1 0.3087 0.3054
1 0.9522 0.9515
1 O9522 0.9515
Responsible climatic and spatial
variables to outline suitable climate
spaces
Principal Component Analysis (PCA) underscored the
complex interplay of climatic and spatial factors driving
the distribution and habitat suitability of D. russe/ii in
Bangladesh. It identified three components (PC1, PC2,
and PC3) that collectively explained over 79% of the
variance in the occurrence of D. russelii. These compo-
nents encompassed 15 significant variables (loading value
> 0.7), which either positively or negatively influence the
species distribution (Table 3).
PC] accounted for the largest variance and highlighted
key variables influencing the species distribution. Positive
contributors included minimum temperature of the coldest
herpetozoa.pensoft.net
144 Najmul Hasan et al.: Expanding habitat suitability of Russell's viper in Bangladesh
92°F
24°N 26° N
22° N
92°E
92° E 88° E 90°
24°N 26° N
22° N
88° E 88° E
90° E 92° E
88° E 90° E
88° E 90° E
90° E
92° E
88° E
90° E 92° E
24° N 26° N
22° Ty
92° E 88° E 90° E 92° E
N
92° E
Zz Ww E
&
Les
S
> 1 in = 123 miles
°. 03060 120 180 240
a ees Viles
Daboia russelii
92° E
Figure 2. Occurrence records of Daboia russelii in new localities in Bangladesh, illustrating its dispersal pattern: A. In 2019;
B. 2020; and in C. 2021, this species was observed along the riverine channels of the Padma and Meghna Rivers; D. Since 2022,
this species has occurred in new localities independent of river channels; E. In 2023, the species had reached coastal districts in the
southwestern region of the country.
month (0.937), annual precipitation (0.805), precipitation
of the driest month (0.942), and precipitation of the driest
quarter (0.905). Conversely, variables with negative influ-
ences included mean diurnal range (-0.941), temperature
seasonality (-0.920), temperature annual range (-0.868),
and elevation (-0.724). PC2 identified additional variables
affecting the distribution of D. russelii. Positively associat-
ed factors were annual mean temperature (0.725) and max-
imum temperature of the warmest month (0.722). In con-
trast, negative influences came from isothermality (-0.737)
and precipitation of the warmest quarter (-0.935).
Sex-based population structure
Over a four-year study period, the collected individuals
of D. russelii exhibited a distinct female-biased trend
(Fig. 5). The trend lines in Fig. 5 further support this ob-
servation, showing an upward trajectory for females and
herpetozoa.pensoft.net
a corresponding decline in males. The high coefficient of
determination (R? = 0.98) for both male and female trends
suggest a strong, consistent pattern in the sex ratio dy-
namics over the analysed period. In 2019, the sex ratio of
collected specimens was balanced at 1:1, indicating equal
male and female representation. By 2020, females began
to outnumber males with a ratio of 1:1.3, reflecting an
increase in the female proportion to approximately 56.5%
of the sample. This female dominance became more pro-
nounced in 2021, with females accounting for 66.7% of
the population and a sex ratio of 1:2 favouring females.
Role of predators and competitors in
population expansion
The apparent population expansion of D. russelii in
Bangladesh may also be influenced by a significant de-
cline in both its predators and competitors. Specifically,
Herpetozoa 38: 137-153 (2025)
88 89 90 91 92
145
0.4
0.3
0.2
0.1
88 89 90 91 92
Figure 3. Suitable climate map of D. russelii in Bangladesh. A. Weighted present suitable climate space (0.7* Maxent current) +
(0.3* Bioclim current). B. Weighted future (2080) suitable climate area (0.7*Maxent future) + (0.3* Bioclim future).
Currently suitable
Suitable in future
Commonly suitable
Currently unsuitable but suitable in future
Currently suitable but unsuitable in future
Commonly unsuitable
Currently unsuitable
Unsuitable in future
% of country area
Wi Suitability indices §§ Unsuitability indices
Figure 4. Suitability index based on weighted average ensemble of Bioclim and Maxent for present and future climate areas (0.7 *
Maxent) + (0.3 * Bioclim) shows that currently 23% of the area are suitable and the remaining 77% unsuitable for Daboia russelii
in Bangladesh. In the future, 79% of the country area is suspected to be climatically unsuitable.
the population of predators has declined by 29%, while
competitors have seen a more substantial decline of 46%
(Fig. 6A, B). Notably, the status of many species remains
uncertain, with 36% of predators and 32% of competitors
categorized as “unknown” according to IUCN (2015).
Conversely, only a small proportion of species—4%
of predators and 1% of competitors—have shown an
increasing population trend. Threat levels are also con-
cerning, with approximately 14% of predators and 11%
of competitors regionally classified as threatened or
near-threatened (CR, EN, VU) by IUCN Bangladesh
(2015) (Fig. 6C, D). Additionally, 18% of predators and
19% of competitors are classified as Near Threatened
(NT) due to declining population trends.
Role of land use type in habitat
selection
The analysis of habitat selection based on land use in-
dicates a pronounced trend toward increasing rice culti-
vation over the past two decades. Specifically, gross rice
production has shown a rapid increase with a strong cor-
relation (R* = 0.93) between time and production trends
(Fig. 6E). Between the fiscal years 2001-02 and 2021-22,
the cultivated area dedicated to rice expanded modestly by
0.49%, while total rice production surged by 2.32%. This
reflects an intensification of agricultural practices, likely
driven by higher yields per year rather than a significant
expansion in cultivated area. Greater and more frequent
herpetozoa.pensoft.net
146
co
f)
R? (male)= 0.98
R? (female)= 0.98
% of sample
as (o>)
oO oO
NO
(=)
2019
WY Male ™ Female
» Female trendline = =
Najmul Hasan et al.: Expanding habitat suitability of Russell's viper in Bangladesh
Male trendline
Figure 5. Sex-based population structure of Daboia russelii collected in Bangladesh from 2019 to 2021 suggests a gradual increase
in females in natural habitats.
Table 3. Loading scores of different variables in Principle Component Analysis (PCA).
Variable Name Description
Bioclim 1 Annual mean temperature
Bioclim 2 Mean diurnal range
Bioclim 3 Isothermality
Bioclim 4 Temperature seasonality
Bioclim 5 Max. temperature of warmest month
Bioclim 6 Min. temperature of coldest month
Bioclim 7 Temperature annual range
Bioclim 12 Annual precipitation
Bioclim 14 Precipitation of driest month
Bioclim 15 Precipitation seasonality
Bioclim 17 Precipitation of driest quarter
Bioclim 18 Precipitation of warmest quarter
Spatial 1 Elevation
Spatial 2 Bio-ecological zones
Spatial 3 Climatic sub-regions
Spatial 4 Flood plain
Spatial 5 Forest types
Spatial 6 Land use
Spatial 7 River zones
availability of rice, for example, due to multiple planting
and harvest cycles per year, 1s expected to result in high-
er rodent populations which in turn could sustain higher
populations of rodent-eating snakes like D. russelii.
Role of flooded areas in dispersal
Over the last two decades, Bangladesh has shown an in-
creasing trend in flood-affected lowland areas (Fig. 6F).
Notably, major flood events in 2004, 2007, 2017, and 2020
impacted 38%, 42%, 42%, and 40% of the country’s total
area, respectively. These data indicate a consistent rise in
the extent of flood-affected regions. Floods can facilitate
the terrestrial species over the inundated landscape.
Discussion
Our study confirms a synergistic effect of several cli-
matic and spatial variables on the geographic expansion
of Daboia russelii in Bangladesh, with a female-biased
herpetozoa.pensoft.net
PC1 PG@2 PC3
0.592 QO. 725 0.022
-0.941 0.269 -0.051
-0.406 -0.737 -0.227
-0.920 0.315 0.090
-0.670 Og 22 0.039
0.937 -0.034 0.066
-0.868 0.467 -0.007
0.805 -0.482 -0.027
0.942 -0.079 0.077
-0.570 -0.255 0.700
0.905 0.315 0.001
0.087 -0.935 -0.114
-0.724 -0.356 0.386
0.492 0.421 -0.197
-0.103 0.073 -0.854
0.115 -0.063 -0.498
0.566 0.079 0.690
0.643 0.174 0.417
-0.726 -0.335 0.094
population structure. The IUCN Red List assessment
has documented an increasing distribution trend of this
viper in 2015 (IUCN Bangladesh 2000; Rahman 2015).
Our species distribution models revealed that the real-
ised climatically suitable areas are four times larger than
the observed ranges in 2015 (Rahman 2015). So, these
suitable climate spaces that exist beyond the currently
observed distribution of this viper may provide potential
for further dispersion into suitable climatic zones in the
near future as suitable climate significantly influences
snake populations and their distribution (Muthoni et al.
2010; Archis et al. 2018; Chowdhury et al. 2022). Being
a proficient swimmer, D. russelii is capable of travelling
long distances using water currents and floating debris
through river channels (Warrell 1989), which is pre-
dominantly effective in riverine Bangladesh. In addition,
floodwaters in this flood-prone country create temporary
connections between lentic and lotic water bodies, nota-
bly facilitating dispersal pathways for good swimmers
like D. russelii to move across flooded areas and explore
new habitats (Lesack and Marsh 2010). In addition, there
are no high-elevation geographical barriers between the
Herpetozoa 38: 137-153 (2025)
30 40
wa w
2&2 & 30
3 3
a, 20 o.
wn wm
io ‘5 20
10
| a a ry oe
a wf ig. 8 a § 8 8 38
3 2 73) = 2 3 Q nv S 3
a P A a + ee A
Population trend (predators) trend (competitors)
a
3
25 . . .
=| Rice cultivation e
ou ee
s o
8 70 S
s =e
22 =:
= 15] R? (total production) = 0.93 3
= 5
§ OOO mg gg gO OPO 0-0-0 Ong OOOO 3
a) i
a 10
R? (gross area) = 0.65 B
agntnenwacaranmtnwonwxanonuida
Tee sr 1) rel itp en cr go) ee bry sik ee Mego one oe cielke die reatee Sik
Ta mM THY ere OH Se ANmntrtrnveonr oan co a
oO co ococohc co 9G 8G fs ff Ss se se st se ese eS = aa
Seseege 5c SESE SE SESS esosecss S
aaaangnqgqrqrdrananaatqaqaaqaaaa
=== Gross area === Total production
Trendline (gross area) = = Trendline (total production)
% of species
147
60
Nn
So
% of species
>
o
bo
i=)
all é
EB a 18
status (predators)
ia
5 fi
Affected area (%)
(Wy OOO) Bare poyalpy
=O= Affected area (*1000 km?) FE] Affected area (%)
Trendline
Figure 6. Decreasing population trends of potential predators (A) and competitors (B) might facilitate population expansion of
Daboia russelii. A total of 32% of potential predators (C) and 30% of potential competitors (D) were assessed under threatened or
near threatened categories regionally by IUCN Bangladesh in 2015. Lists of potential predators and competitors of D. russelii with
their population trends and status are provided in Supplementary material 3 and 4, respectively. E. Increasing trends of land use
for rice cultivation and gross production of rice over the years in Bangladesh (2001-02 to 2021-22) provided additional paddy field
habitat for D. russelii and more food for their rodent prey. F. Flood affected areas in Bangladesh over the last 20 years (2001-2020)
might provide dispersal pathways for D. russelii towards low plains.
observed distribution and suitable climate spaces that can
ease the dispersion (Chowdhury et al. 2022). These find-
ings suggest a strong influence of climate and biophysical
factors on this snake’s expansion.
In addition to inhabiting favourable climate spaces,
D. russelii will find surtable cropland habitat, especially pad-
dy fields in agrarian Bangladesh. The recent increasing culti-
vation of paddy fields in Bangladesh, to meet the demand for
this staple food for the vast human population of the country
(Jalilov et al. 2019), provides favourable habitats for D. rus-
selii. The introduction of hybrid rice varieties and improved
irrigation have led to multiple rounds of rice cultivation
throughout the year (Tiongco and Hossain 2019), enhancing
the habitat suitability for this viper by providing abundant
prey and shelter (Wuster 1998), as well as camouflaged
hiding places for escaping predators (Moré et al. 2024), and
suitable conditions for daily activities (Glaudas 2021). Small
mammals such as rodents, crabs, frogs, and birds are signif-
icant food sources for adult and juvenile D. russel/ii (Wuster
1998; Rahman 2015; Khan 2018). The availability of prey
is directly correlated with the healthy body and reproductive
success of snake species (Brown et al. 2017). In addition,
reduced predator and competitor populations may further
support the population expansion of this species, leading to
a higher prevalence in the country. In combination, widely
suitable climatic conditions (Chowdhury et al. 2022), an-
thropogenic land use changes (Webb and Shine 1997), and
increased availability of prey (Bonnet et al. 1999) are likely
to be strongly positive influential factors for the occurrence
of this viper in large parts of Bangladesh, and for its disper-
sal into previously unoccupied localities.
We assume that males and females have equal expo-
sure and likelihood of being found by humans. Howev-
er, among our field-collected D. russelii from 2019 to
2021, we observed an increase in the proportion of fe-
males, suggesting a potential female-biased population
structure for this viper in Bangladesh. A female-dom-
inant population, along with the species’ ovovivipa-
rous mode of reproduction, high fertility rate, and large
clutch sizes (6—63 live offspring), might also facilitate
rapid population growth (Daniel 2002). Moreover, it is
tempting to speculate whether increasing temperatures
in Bangladesh over recent decades (Rahman and Lateh
2016) might have favoured the production of female
offspring through temperature-dependent sex determi-
nation (Bull 1980) since temperature thresholds during
herpetozoa.pensoft.net
148 Najmul Hasan et al.: Expanding habitat suitability of Russell's viper in Bangladesh
the incubation period can lead to the development of
either male or female offspring in reptiles including
snakes (Charnier 1966). Whether or not this plays a role
in D. russelii warrants further scientific investigation.
While this viper species benefits from currently avail-
able climate spaces in Bangladesh, projected climate
changes for the future may reduce suitable climate spac-
es, particularly in northwestern and central regions of the
country. Temperature and precipitation emerged as signif-
icant factors in shaping suitable climate space for snake
species (Wu 2016; Chowdhury et al. 2021, 2022), and
this is also observed here for D. russelii. As poikilother-
mic animals, the physiological processes of snakes, such
as reproduction and metabolism (Teixeira and Arntzen
2002), are influenced by ambient temperature and precip-
itation (Aubret and Shine 2010). We found that the tem-
peratures of the cold season and precipitation in the dry
season positively influence the distribution of D. russelii
in Bangladesh, while seasonal temperature fluctuations
and lower annual precipitation negatively impact its dis-
tribution. In the face of rapidly advancing climate change,
these factors could contribute to the decline of suitable
climate spaces for this species in the future.
As D. russelii is a highly dangerous, medically im-
portant venomous snake species, its observed geographic
range extension, and the likelihood of its presence in, or
dispersal to, additional suitable areas of Bangladesh, pose
significant public health concerns. These are reflected
by increased reports of morbidity and mortality due to
envenoming by this species from different locations of
Bangladesh (Haidar et al. 2023; Amin et al. 2024). Those
reports further suggested that this snake species may have
spread to as many as 27 out of the 64 districts in the coun-
try. The presence of D. russe/ii in agricultural landscapes
and resulting snake-human conflicts (Jaman et al. 2020)
also causes fear among farmers (Rahman et al. 2010). On
the other hand, lack of awareness of the presence of this
highly venomous snake can lead to insufficient preven-
tive practice and allocation of healthcare resources for
the management of D. russelii envenoming. Our research
identifies additional areas of Bangladesh where this spe-
cies is likely to occur, and field workers and farmers as
well as public health and healthcare professionals in these
areas should be informed about the possible presence of
this viper and recommended preventive practice. Public
awareness campaigns and wearing protective gear during
agricultural work are critical to mitigate risks. Victims
must be educated to prioritize seeking modern health-
care facilities for effective treatment. We recommend
that health policymakers consider the directional trends
in the expansion of this venomous snake to implement
preventive measures and allocate resources effectively to
enhance public health safety.
At the same time, human-snake conflict in a country
with a high human population density 1s a limiting factor
for the dispersal of snakes (Glaudas 2021). The fearful and
ageressive attitude towards snakes (Jaman et al. 2020) of-
ten results in snake killings which may lead to unnoticed
herpetozoa.pensoft.net
declines of their populations. In the face of this, the pro-
jected reduction of future suitable climate spaces for this
species in Bangladesh should raise concern for conser-
vationists. While it is imperative to urgently implement
measures to minimise fatalities caused by this species,
through effective snakebite management emphasizing
public awareness, mitigating snake-human conflicts, im-
proving preventive practices and provision of healthcare
for snakebite patients especially in rural areas, develop-
ing efficacious policies to ensure the sustainable surviv-
ability of D. russelii in the future is also very important.
In recognising the limitations of this research, we
suggest that incorporating a broader range of ecological,
climatic, and anthropogenic factors could enhance our
understanding of the rapid expansion of venomous spe-
cies. A longer-term field study beyond the four years of
observation and collection could provide more precise
insights into the dispersal patterns and sex ratio of this
viper. Although we assumed equal capture probability for
male and female vipers, further research on the capture
efficiency of male and female D. russe/ii would provide a
more accurate assessment of the true male-to-female ra-
tio in the wild population. Such comprehensive analyses
are crucial not only for effective conservation and public
health management in Bangladesh but also for addressing
similar challenges posed by venomous species globally,
particularly in regions experiencing parallel ecological
and climatic shifts.
Conclusion
The highly venomous D. russelii, one of the world’s most
medically important viper species, has a much larger geo-
graphic distribution in Bangladesh than previously docu-
mented and it appears to be expanding its population and
range into new areas of this country. We explained the
climatic and environmental factors, with high cold-sea-
son temperatures and dry-season precipitation as well as
human land-use changes creating optimal habitats for this
snake. As the observed distribution of this species so far
covers only a portion of the climatically suitable spaces in
Bangladesh, it is expected to already occur in certain addi-
tional regions and/or to be able to disperse to these in the
near future. The snake’s strong swimming capability al-
lows it to utilise river currents for range expansion partic-
ularly during the monsoon season, with temporary flood-
plains subsequently becoming viable dry-season habitats.
Terrestrial dispersal is facilitated by the absence of phys-
ical barriers, and newly occupied habitats often feature
croplands and grassy vegetation, offering abundant prey
and minimal predators. However, projections indicate a
shrinking of climatically suitable habitats in the future
due to seasonal temperature variability and reduced pre-
cipitation. As the medical relevance of D. russelii and as-
sociated human-wildlife conflict also lead to the targeted
killing of snakes, this ecologically and economically im-
portant predator of rodents 1s also exposed to significant
Herpetozoa 38: 137-153 (2025)
anthropogenic threats. Proactive management strategies
must mitigate the impacts of snakebite to prevent mor-
tality and morbidity of the envenoming bite of this viper.
Acknowledgements
We are grateful to all members of the Eco-climate Lab,
Department of Zoology, University of Chittagong, Chatto-
gram, Bangladesh, for their help during this research. We
are also thankful to Borhan Biswas Romon, Md. Sahidul
Islam, Mohammad Shahjahan, and Sharif Rajon for their
co-operation during fieldwork and responding to rescue
call. We extend our gratitude also to the Venom Research
Centre, Bangladesh, for providing Russell’s viper data.
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Supplementary material 1
The Seven spatial variables and their
categories used for the current analysis
Authors: Najmul Hasan, Joya Dutta, Mohammed Noman, Md.
Mizanur Rahman, Sajib Rudra, Abdul Auawal, Md. Rafiqul
Islam, Md. Asir Uddin, Harij Uddin, Md. Towfiq Hasan, Md.
Farid Ahsan, Ulrich Kuch, Aniruddha Ghose, Ibrahim Khalil
Al Haidar, Mohammad Abdul Wahed Chowdhury
Data type: docx
Copyright notice: This dataset is made available under the Open
Database License (http://opendatacommons.org/licenses/
odbl/1.0/). The Open Database License (ODbL) is a license
agreement intended to allow users to freely share, modify,
and use this Dataset while maintaining this same freedom
for others, provided that the original source and author(s)
are credited.
Link: https://doi.org/10.3897/herpetozoa.38.e143411.suppl1
Supplementary material 2
ODMAP document
Authors: Najmul Hasan, Joya Dutta, Mohammed Noman, Md.
Mizanur Rahman, Sajib Rudra, Abdul Auawal, Md. Rafiqul
Islam, Md. Asir Uddin, Harij Uddin, Md. Towfig Hasan, Md.
Farid Ahsan, Ulrich Kuch, Aniruddha Ghose, Ibrahim Khalil
Al Haidar, Mohammad Abdul Wahed Chowdhury
Data type: csv
Copyright notice: This dataset is made available under the Open
Database License (http://opendatacommons.org/licenses/
odbl/1.0/). The Open Database License (ODbL) is a license
agreement intended to allow users to freely share, modify,
and use this Dataset while maintaining this same freedom
for others, provided that the original source and author(s)
are credited.
Link: https://doi.org/10.3897/herpetozoa.38.e143411.suppl2
Supplementary material 3
Predators of Daboia russelii in Bangladesh
Authors: Najmul Hasan, Joya Dutta, Mohammed Noman, Md.
Mizanur Rahman, Sajib Rudra, Abdul Auawal, Md. Rafiqul
Islam, Md. Asir Uddin, Harij Uddin, Md. Towfigq Hasan, Md.
Farid Ahsan, Ulrich Kuch, Aniruddha Ghose, Ibrahim Khalil
Al Haidar, Mohammad Abdul Wahed Chowdhury
Data type: docx
Copyright notice: This dataset is made available under the Open
Database License (http://opendatacommons.org/licenses/
odbl/1.0/). The Open Database License (ODbL) is a license
agreement intended to allow users to freely share, modify, and
use this Dataset while maintaining this same freedom for others,
provided that the original source and author(s) are credited.
Link: https://doi.org/10.3897/herpetozoa.38.e143411.suppl3
Herpetozoa 38: 137-153 (2025)
Supplementary material 4
Competitors of Daboia russelii in Bangladesh
Authors: Najmul Hasan, Joya Dutta, Mohammed Noman, Md.
Mizanur Rahman, Sajib Rudra, Abdul Auawal, Md. Rafiqul
Islam, Md. Asir Uddin, Hartj Uddin, Md. Towfiq Hasan, Md.
Farid Ahsan, Ulrich Kuch, Aniruddha Ghose, Ibrahim Khalil
Al Haidar, Mohammad Abdul Wahed Chowdhury
Data type: docx
Copyright notice: This dataset is made available under the Open
Database License (http://opendatacommons.org/licenses/
odbl/1.0/). The Open Database License (ODbL) is a license
agreement intended to allow users to freely share, modify,
and use this Dataset while maintaining this same freedom
for others, provided that the original source and author(s)
are credited.
Link: https://doi.org/10.3897/herpetozoa.38.e143411.suppl4
t52
Supplementary material 5
Predicted suitable climate for Daboja russelii in
current and future (2080) climate scenario
Authors: Najmul Hasan, Joya Dutta, Mohammed Noman, Md.
Mizanur Rahman, Sajib Rudra, Abdul Auawal, Md. Rafiqul
Islam, Md. Asir Uddin, Harij Uddin, Md. Towfiq Hasan, Md.
Farid Ahsan, Ulrich Kuch, Aniruddha Ghose, Ibrahim Khalil
Al Haidar, Mohammad Abdul Wahed Chowdhury
Data type: docx
Explanation note: Suitable climate map of Daboia russelii in
Bangladesh. Present and future (2080) suitable climate
Space predicted by Bioclim and Maximum Entropy (Max-
ent) Model.
Copyright notice: This dataset is made available under the Open
Database License (http://opendatacommons.org/licenses/
odbl/1.0/). The Open Database License (ODbL) is a license
agreement intended to allow users to freely share, modify,
and use this Dataset while maintaining this same freedom
for others, provided that the original source and author(s)
are credited.
Link: https://doi.org/10.3897/herpetozoa.38.e143411.suppl5
herpetozoa.pensoft.net
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